SP OXTAXEO US-GENERA TIOX CONTR VERS Y. 457 



posed of phosphate of potash, sulphate of magnesia, triple basic phos- 

 phate of lime, tartrate of ammonia, and distilled water. If these in- 

 gredients are all mingled the fluid becomes speedily charged with 

 bacteria, unless hermetically sealed, and sometimes even then. We 

 therefore keep the ammonia in a separate solution, mixing them when 

 required. 



A portion of the fine dust of the maceration was now taken and 

 thoroughly scattered through the air of the prepared chamber. The 

 condensed beam from an oxyhydrogen lime-light 1 was then sent 

 through it. Its line of passage was far more brilliantly marked inside 

 the chamber than in the outer air. It was deemed inexpedient to 

 insert the fluids while such brilliant points were visible in the air, and 

 four hours were suffered to elapse. The lime-light beam was still 

 visible with perfect distinctness, but its path within the chamber was 

 much less brilliant and more homogeneous than it was without. The 

 fluids were then carefully mixed, and five small glass basins of the 

 mixture were inserted. The whole was undisturbed for five days. 

 At the expiration of that time the beam of the lime-light sent through 

 the chamber was absolutely invisible, although perfectly clear in the 

 open air on both sides of it. 



The fluids were now withdrawn. Ten "dips" were taken out of 

 each basin for microscopical examination. In every "dip" that is, 

 fifty in all one or other of the monads appeared, and were in a state 

 of active fission / and in twenty-seven of the "dips" both monads 

 were found. Bacteria swarmed the field, which of course I fully 

 expected. 



I now took five other glass vessels, and inserted them with great 

 care into the now moteless air of the chamber, and poured in, as be- 

 fore, fresh Cohn's fluid. They were exposed for another five days. 

 On careful microscopical examination of seventy-five " dips " not a 

 single monad of either form appeared ; bacteria were feebly present, 

 but of course no steps were taken to guard against these, and, as be- 

 fore, they were anticipated. 



The air of the chamber was again impregnated with dust, as be- 

 fore suffered for a time to settle, and these same vessels of fluid, which 

 had yielded negative results, were again placed in the chamber. At 

 the expiration of five days they were again examined, and one or 

 other of the monads was found in every successive "dip." 



Now let it be observed that there can be no possible error as to 

 the forms. They were the identical species of the maceration, with 

 which I am as familiar as with a barn-door fowl. What, then, is the 

 logic of these facts ? Dr. Tyndall proves that bacteria only develop 

 in sterilized infusions when the air around them is laden with motes 

 of incalculable multitude and exquisite minuteness. Given the pres- 



1 This was of course very much less capable of " searching " than the electric beam ; 

 but it served for the rougher end I had in view. 



